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Does a windmilling propeller create more drag than a stopped propeller in an engine out scenario?
For this question lets assume that we are talking about a fixed pitch propeller and not a variable pitch propeller.  I do understand that variable pitch props should be feathered during an engine failure.
The main rationale for this question is this statement that I found on the Pilots of America forum:

I've been doing some research on something I hard from my old chief CFI a couple years back, but I'm not finding much on it. He is the only person I've heard this from, and any CFI, DPE, ect. I've talked about this to since have not heard of it. That being that when you have an engine failure more than several thousand ft. with a non-full-feathering prop, that you should pitch up and decrease airspeed, sometimes to an intentional stall, to stop the rotation of the prop/engine. (Of course, only after you have attempted to restart.) The reason being that you will see a greater gain in glide distance by reducing the drag created by forcing thee air to turn over the engine. He claimed that while you would most likely be off of Vl/d for a short amount of time, thus not gliding in the most efficient manner, that is outweighed by the decrease in drag. (As I said, do this only with several thousand feet and plenty of time.) He claimed that in the case of something such as a 172, doing this procedure at, say 10,000ft, you would gain several more miles of glide distance.

So what I am asking for is if indeed a windmilling prop has more drag than a stopped prop and if so would it be beneficial to follow the advice in the pilot forum?

I would be surprised if something like a 172 would windmill the prop at all, especially where the air is thinner at 10,000 feet. A lot of times engine failure means the engine locks up. Fuel starvation (more common) can let the prop spin, but there is a lot of force needed to spin a prop. I think a spinning prop is a lot more common on aircraft that don't have direct drive, like a turbo prop than it is for direct driven propellers.

Most GA twins can fly with a feathered prop.  They will not windmilling prop.  Yes...the windmilling prop generates a HUGE amount of drag.

There are some situations such as model airplanes/ sailplanes with brushless electric motors where the answer is not cut-and-dried and depends on many variables.

Yes a Cessna 172 can definitely keep the prop windmilling.  You have to slow to near stall speed to stop it.  After that you can speed up and it won't windmill till you get going rather fast.  I'm sure the drag is less with the prop stopped in that case.

Air density probably doesn't matter, if we are talking about the tendency of the prop to windmill at any given IAS.

I soared a Cessna 152 for over an hour with the prop stopped btw in mild mountain wave conditions.

I doubt this advice is correct. For one thing I'd want the propeller to keep turning so I can continue to try to restart the engine when I can do so during the descent. For another, I have never seen any evidence that a propeller will generate more drag if it is turning than if it is stopped.

@JuanJimenez it is quite a well-known effect.

Windmilling propeller can even have less drag: http://www.peter2000.co.uk/aviation/misc/prop.pdf

@quietflyer No, it is not. It has been shown through testing that the answer is "it depends." At any rate, if you lose power it's just dumb to raise the noise and dump what energy you have just to stop the prop. I find it amazing a CFI would suggest that.

@JuanJimenez that's quite a blanket statement that you made there.  If the engine is simply not restartable by any means and you have a fair bit of altitude but lots of nasty terrain below, management of your instantaneous kinetic energy is not your issue, rather management of your glide ratio over the long run is your issue.  Obviously stopping the prop is not something you are going to be thinking about if the engine quits at 200' AGL.  As an aside I'd say it would seem to take a very un-curious pilot to never have intentionally stopped a prop in flight.

For example, if you've run out of fuel

@Erbureth That experiment was done using a tiny wind tunnel (15 cm x 15 cm x 50 cm) at very low flow velocity (max of 5 m/s = 9.72 knots.) Honestly, I wouldn't take its results to apply to real-world airplanes at all. I strongly doubt that a < 15 cm prop in < 10 knot flow reasonably models a ~200 cm prop in ~100 knot airflow.

@quietflyer The research has already  been done and the answer is clear, it depends. If you have empirical data to refute the research, post the link.

@Juan, it doesn't need an experiment. It is an unquestionable, logical application of a principle of physics that is a core basis for almost everything we know about how things work. The principle of "Conservation of Energy". Spinning the motor takes energy. That energy has to come from somewhere. It can't simply be created out of thin air. The only things in question are how large is this effect, and whether the process of slowing to stop the prop creates a larger opposite effect.

@charlesbretana ", it doesn't need an experiment". Now where have i heard that before...

@Juan, go jump in your Perpetual Motion FTL time machine and go back to the future. That's apparently, where you heard much of what you believe. I don't know where you went off track, but somehow, somewhere, you did. What you propose is simply not physically possible as we currently understand basic core principle of Physics. I suggest you re-analyze whatever sources you are relying on to see where you misinterpreted, mistook, or misunderstood what they said, or what assumptions they made that are not applicable to real-world analysis.

@CharlesBretana Heard that before too. You really are boring me.

I would not follow the advice in the forum. While the reasoning that a windmilling prop does create more drag is sound, I have seen no empirical evidence that says how much it actually translates to in Feet Per Minute. The only studies I have seen have been inconclusive on the subject, and say there's a number of factors that you can't really control in that situation. The prop isn't that big compared to the airplane itself, so if a spinning one has 30% more drag (just a guess, as I said I've seen no actual numbers) it isn't going to make you plummet out of the sky.
What I would recommend is following the engine failure procedure in the POH of your particular aircraft. The advice to slow the airplane to try and get the prop to stop has a number of flaws:

Distraction from critical tasks: Slowing the airplane until the prop stops is taking your focus away from finding a field to land in, ensuring your passengers are briefed and strapped in, making a mayday call and attempting to restart the engine. You'll be busy enough!
Low airspeed danger: Slowing enough to stop the prop may require a very low airspeed, and you could have a stall/spin excursion, which is far more dangerous than a glide landing
Drag curve: flying very slow to get the prop to stop will put you below best glide speed, which is where you get your best glide ratio. Below best glide speed you start to develop a high rate of descent, so by the time you get the prop stopped you have lost hundreds of extra feet. You could lose more altitude than you would potentially save, and waste valuable time doing it
The chances are good that you couldn't change the prop behavior anyway: if your crankshaft has broken the prop's going to spin no matter what you do, if you've thrown a rod it's going to stop and you couldn't get it to windmill if you flew at mach 1

Doing some math puts this into perspective. Say an airplane's engine-out rate of descent with a spinning prop is 1000, and with a still prop it's 900 fpm. In a glide from 3000ft that buys you an extra 20 seconds, but it probably takes a lot more than 20 seconds to slow enough to stop the prop and then regain a stable airspeed.
Flying very slow to stop the prop is a potentially dangerous distraction, just set best glide speed and if the prop stops its a bonus.

"flying very slow to get the prop to stop will put you below best glide speed, which is where you get your best glide ratio. Below best glide speed you start to develop a high rate of descent" This is wrong.  Minimum sink glide is normally significantly slower than best glide (by 20 knots or so).  If you slow to stop the prop, you'll lose less altitude doing it, not more, unless you slow so much you stall.  Obviously, don't stall.

I believe the answer also concern the glide distance you can get, not just rate of descend.

The answer: it depends. Generally, a stopped propeller will be stalled, and so creating little drag. A windmilling propeller, conversely, usually will not be stalled, will be extracting energy from the airstream, and using that to turn the engine (which typically takes a moderate amount of energy), which will increase sink rate.
However, should you stop the propeller? That's a much harder question. Relevant questions are: how slow must you go to stop the propeller? Can you stop the propeller? If it requires dropping below minimum sink speed for an extended period, it is probably a bad idea, as sink increases rapidly with decreasing speed (you're on "the backside of the power curve" any time you're flying below minimum sink speed).
On some antique aircraft, it is or was reputed to be a requirement in some clubs that pilots be able to stop the engine and prop and restart the engine in flight before being granted pilot privileges for, say, the club Tiger Moth (these are generally hand-started). It is widely claimed that stopping the prop does extend the glide noticeably. The Tiger Moth also has a large, slow-turning wooden prop, and a fairly low stall speed.
As for whether I would try this in an emergency? Almost certainly not; if it's the POH, then sure... but I've never seen it in the POH of any single engine aircraft I've ever flown. And if I'm flying engine out, I've probably got worse things to worry about (unless I'm flying my more-usual gliders).

Welcome to Aviation.SE! A good first post. If you haven’t already done so, I’d recommend checking out the [help] and taking our [tour] so you can see how the site works.

I'm physicist, but not a pilot (yet). I don't see why windmilling prop would "extract" any more energy than stopped. The most energy needed is to accelerate blades rotation, which were spinning before anyway, so the only energy left is internal engine rotation friction, which I think is minuscule. But windmilling prop blades have smaller attack angle, so would produce less total drag. Probably worth a separate question here.

@DzmitryLazerka Engine friction is not negligible; try releasing the throttle in a car at a high engine RPM, you will see how significant engine braking is (when you will then press the clutch, the remaining deceleration due to drag and rolling resistance will be much less). In an aircraft, instead of the wheel, it's a prop that cranks the engine. Actually, the "lift" produced by prop blades acts parallel (or anti-parallel) to the aircraft's drag. Since a stationary propeller is stalled, its blades don't produce as much "lift" as the unstalled blades of a windmilling prop.

@DzmitryLazerka Even a windmilling propeller's blades can produce zero "lift", provided the blades are at zero-lift AoA. This would be the case if engine resistance was zero, but it's not.

Thank you, sounds good, although I'd say engine braking in car only works if the throttle is closed (creating vacuum in cylinders). If the throttle is open, air flows freely into-out of cylinders.

@DzmitryLazerka The braking is significant even in diesel cars which have no throttle (diesels are controlled by fuel metering only) nor braking valves (they stopped making those because it was too noisy).

@DzmitryLazerka Air doesn't "flow freely" through a piston engine under any circumstances because the valves are in the way. The air will still get compressed during every compression stroke (thus braking and storing the energy in the compressed air), but the following expansion stroke is not an exact reverse of the compression stroke, so it does not recover all the energy (some of it is converted to heat in the engine block and exhaust air), yielding net braking.

A windmilling propeller creates much more drag, by an order of magnitude at least. The obvious example is an autogyro or helicopter in autorotation, which drops like a stone if the rotor stopped.
Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one. The difference is most pronounced for large rotors with few blades and almost nonexistent for turbofans. This answer gives some numbers:

If we compute the lift component per area of a vertically autorotating rotor, it is comparable to a coefficient of 1.1 to 1.2 referenced to the rotor area. According to this source, a flat plate has a drag coefficient of 1.28 and a parachute has one of 1.4. So in vertical descent, the auto-rotating rotor is almost as good as a parachute of the same area.

If you are high enough when the engine stops, it's a good idea to slow down a little so that the propeller stops windmilling. Once it has stopped, you can accelerate back to normal. The propeller will usually not start windmilling again, as it's drag, and thus available power, is now much lower.

Last time I looked at a propeller driven aircraft, the prop wasn't pointing vertically upwards. Also your assertion the windmill makes no difference to the drag of turbofans is plain wrong - a fan that is not freely windmilling has MUCH more drag, as has been demonstrated in real life when engine damage in flight locks up the rotors.

A helicopter in a vertical descent under autorotation is not much different from a propeller aircraft in horizontal flight with one engine inoperative. The rotor faces into the direction of travel and crates 'windmill drag'. The only difference is that the helicopter pilot tries to maximize drag in order to save his life. - @alephzero

An autogyro is a good analogy but I'm not sure the results are the same. The reason wind-milling blades cause more drag is because they're going faster. An autogyro has huge blades and very little other drag. An aircraft has much smaller blades and lots of induced drag from the wing. So while the drag from the prop may be an order of magnitude higher, the total drag will not be.

-1: the claim of an order of magnitude difference, and the claim that drag is a function of the swept area for a windmilling prop, both sound extremely dubious (at least to me). I'd remove the downvote and stand corrected if some evidence or citations to back up the claims can be provided.

@TypeIA The claim is correct. A quantification for helicopters in this answer

@Koyovis It is the drag resistance from falling against an oblique surface that produces the orthogonal component necessary to glide or autorotate.  You may be confusing this force with drag created in the direction of the glide.  But you writings are very interesting and informative, just mis-applied.  Key to creating an oblique surface is moving CG away from Cdrag of a falling object.  The miracle of gliding is how much more efficient the wing airfoil is at slowing the rate of descent, yet the object must keep falling to continue to glide.

@Koyovis thanks for the excellent info anyways.

autogyro and helicopter are poor examples, because their blades have such low pitch.
This paper clearly shows that pitch is the most important factor: http://www.peter2000.co.uk/aviation/misc/prop.pdf

The drag is significantly more for a windmilling propeller.
Both aerodynamic drag and energy lost in the engine contribute.  I estimate you will sink at least 200 FPM faster if you let the prop windmill.
For aerodynamic drag, it's impossible to convert this into a feet per minute estimate because it varies so much with the design of the propeller and the overall drag of the airplane.  But you can see here:
Aerodynamics for Naval Aviators, 1965
(page 149 in the page numbers, or 167 in the PDF) that the drag can increase significantly.
A typical fixed-pitch prop has a pitch of around 15 degrees (more details at bottom).  A constant-speed prop which has lost oil pressure, and is not automatically feathering, is probably more like 5 degrees.  (Feathering props are used on multi-engine planes to reduce drag if one engine fails.  Non-feathering props are used on single-engine planes so if the pitch control fails but the engine still works, you don't lose all your power).  Overall, the actual propeller parasitic (simple aerodynamic) drag increases by up to a factor of 3.  Not orders of magnitude, but it's significant.  Since there's no way for me to estimate how much of the total drag is due to the propeller, all I can say is that this is probably noticeable.  However, if you have a cruise prop, or an adjustable prop set to high pitch, it's possible that it works out close to even, as above 22 degrees, the windmilling prop actually has less drag.
But then there's the extra factor of the drag created by the engine, which is probably much more significant.  It's possible to come up with a reasonable ballpark figure.  Estimation and highschool physics are required.
An airplane without power loses potential energy, in the form of altitude, to drag.  Since the airplane's speed doesn't change, its kinetic energy doesn't either and only potential energy need be considered.  We calculate how quickly energy is drained out of the airplane by the spinning engine.
Work is the amount of energy that is transferred from one place to another, and power is the amount of work over time.  The formula for work (in a rotational system, such as an engine) is torque * theta, where theta is the total angular distance rotated.  Power (watts) is expressed in joules per second, although here I'll figure power in joules/minute because our other time units are also in minutes.  The joule, of course, is the unit of both work and energy.
Assume an airplane weighing 1000kg flying at 1500 meters AGL.  Its potential energy is:
1000 kg * 1500 meters * 9.8 (gravity) = 14,700,000 J (14.7 mJ)

Assuming a propeller windmilling at 200 RPM, the angular velocity is:
2pi radians / revolution * 200 revolutions / minute = ~1260 radians / minute

I estimate the torque, given in newton-meters, is somewhere between 50 and 500 Nm, tending toward the high side.  50 is from my personal experience turning a propeller at slow speeds by hand, it's about that much force; but in the air I think this is extremely optimistic.  500 is a higher estimate, justified as follows.
Single-engine planes such as the Cessna 172 frequently have a 180HP engine.  The propeller normally has enough air-grabbing ability to transfer that 180HP into the air at engine redline of ~2700 RPM.
Converting HP to joules / minute (1 watt = 1 joule/second):
180 HP * (746 watts / HP) * (60 seconds / minute) = 8057 kJ / minute

Assuming the propeller efficiency is relatively constant with RPM, you can convert propeller power delivery capability linearly with RPM:
8057 kJ / minute * (200 RPM / 2700 RPM) = 596 kJ / minute

So the propeller should be able to transfer about 600 kJ / minute back into the engine.  This is in the ballpark of my estimate of 500.  However, as not all the normal engine power goes into the propeller (due to mechanical losses and engine powered accessories) the estimate of 500 seems to be pretty close, and I'm sticking with it for sake of simpler math.  This estimate is pretty seat of the pants - lots of error sources, like variations in propeller efficiency with RPM and being driven in reverse - are ignored.  But if the propeller is less efficient, it dissipates more power - so even my high estimate might be too low.
Back to the engine failure.  The power dissipated by the engine is therefore:
1260 * (50 to 500 or you pick) = 63 kJ to 630 kJ per minute

A Cessna 152 has a sink rate of 725 fpm when flying at best glide with stopped propeller (best glide speeds are normally specified with stopped prop); The Cessna 172 is closer to the mass I am using, and has similar glide performance, so I'll just use that same number.  This is an estimated calculation, anyway.  At 725 fpm descent rate (221 meters per minute) it normally takes 6.78 minutes to bleed off that 1500 meters of altitude you started with.  Dividing potential energy by time:
14,700,000 / 6.78 = 2.168 MJ/min energy loss

At the low estimate (probably reasonable only for an engine that suffered total compression loss but no other damage), losing an additional 63 kJ/min only increases your sink rate by
(2.168 + .063) / 2.168 = 1.029

about 3%, or from 725 fpm to 746 fpm.  You might not even notice this on the instruments, although if you snag on a power line at the last second as a result, you'll certainly notice that.  However, at the high estimate, losing an additional 630 kJ/min would increase your sink rate by:
(2.168 + .630) / 2.168 = 1.29

29%, or from 725 fpm to 935 fpm.  That's very significant.  And this does not even include the extra aerodynamic drag from the spinning prop.  It is only due to the energy lost in the engine.
So, in conclusion: If power fails, stop the prop.
There is, however, one final point.  If you lost power because of a mechanical failure, it's very possible that the propeller will stop all on its own due to whatever damage caused the power loss.  However, running out of fuel is the most common cause of in-flight power loss.  If you run out of fuel, the prop will probably keep spinning unless you stop it yourself.

Pitch angle in degrees is different from the way pitch is normally described, which is measured in inches, where something like 76"x60" would be typical.  You can calculate pitch angle based on the propeller measurements in inches using the formula for helix angle.  If you do, remember propeller pitch is specified at 75% of the diameter of the blade, rather than 100% as in the math textbooks).

Good work.  A glider burns altitude as fuel to create kinetic energy. The wing uses this to more efficiently create lift. From a given altitude and mass, wing efficiency and drag determine how far you glide.  The engine being turned does not affect the glide, the drag from the prop does.  Not much difference there (the spinning one may even have a little less).  But any loss in wing efficiency from prop turbulence will directly translate into loss of glide distance.

This paper provided by Erbureth provides empirical evidence to answer the question.  The short answer is that sometimes a stopped propeller provided less drag and sometimes a windmilling one provided less drag.  This actually makes a lot of sense to me as the drag should be related to the location of the stagnation pressure line on the prop.
A few observations from other answers:

One of the things I always hear when this question is asked is that a rotating propeller turns into a disk and has more area.  This is clearly wrong as the area of a propeller blade is always the same whether it is rotating or not.
When a prop is feathered the prop stops windmilling and the drag is considerably less.  This create the perception that the stopped propeller has much less drag but in reality it is due to the fact that the feathered prop has much less form drag.  The fact that the prop is stopped is not the main reason.

It's worth noting that paper is on model airplanes and their wind tunnel tests are significantly below the normal flight speed. It's findings may still hold true, but I'd say to take it with a grain of salt.

Work = force x distance, and a spinning prop goes much farther, so to speak, then a non-rotating one for the same velocity of aircraft. So while the blade area is the same, the spinning makes a big difference in the physics of the problem.

The clue is in the paper: they let the spinning prop freewheel without any resistance. An autorotating helicopter is still providing lift, and chopping away to push that air down.

In other words: torque is the differentiator. Rotation * torque = energy extracted. No torque, no energy required.

The paper is great. I suspect that prop solidity also important, 2 blades thin props will have less windmilling vs locked drag ratio than 3 blades props.

The argument that the windmilling prop is slowing the plane down by extracting energy to turn a dead engine ignores the fact that a frozen prop tries to turn the whole plane.  The control inputs to keep the plane level are probably very close, and the turning airfoil may actually be slightly less draggy, so what is going on here?
It is well known that props are airfoils, and turbulence created by one blade affects the other.
In the windmilling case, the turbulence created by the propellor has a greater affect on that other airfoil, the wing.
This is mostly likely the major factor in loss of gliding distance.  Important to realize the air that the plane is gliding through has no kinetic energy to extract, it's all in the kinetic and potential energy of the plane.  But the windmilling prop does lower the efficiency of the wing in using the planes energy by creating more turbulence.

First sentence: it tries but doesn't succeed, so it's not doing any work on the plane.

It (unmoving) produces drag, a force on the plane.  So does the moving one.  WRT forces affecting the glide, that is what matters.  Turning the engine is work by definition (net movement of engine from force) but the movement of the engine does not affect glide.  The turbulence created by the rotating prop (which we COULD say is energy extracted from the glide forces) does.

Thank God somebody mentions the fact that a frozen prop results in a torque exerted on the plane as a whole. I was going mad reading forum after forum discussion on this topic with nobody ever pointing this out. As for the turbulence hypothesis, wouldn't this mean a pusher prop configuration should show no difference in drag between fixed and freewheeling? Somehow I doubt it...

This is a very good point.  There still could be some effects on the Hstab, causing it to oscillate in pitch, as compared with frozen, or better yet, frozen and feathered.  May be Piaggio though of this in their designs.

I have tested this multiple times in a C152.  Starting at 10,000 feet and cutting off the fuel to the engine -applying nose up to hold altitude as long as possible (thereby slowing my forward speed) until stopping the propeller.  Then gliding with the propeller stopped for quite a distance, passing over multiple airports in the process.  A windmilling propeller left me short by a significant distance.
I know I was weird in my younger days, but I was flying!

It depends on the blade angle
Here's a picture from a very old report:

This is of course specific to the particular rotor and the flow condition at which it was tested, so the magnitude of the numbers on the y axis will be very different for different situations, but the general picture is likely similar for most propellers:

If the prop is feathered, that's always best (duh, we knew that).
Low blade angles are worst (also clear)
If it is at very low blade angles, then having it locked is best
In between: a spinning prop is actually better!

Number 3 and 4 deserve some explanation:
High blade angles
This one is fairly obvious: In completely feathered state (and assuming the blades had no twist), there is no force on the blades except a bit of drag caused by the prop airfoils at zero incidence.
Of course the blades are twisted, so they are pushing air around circumferentially a little.
If the blade angle is reduced a bit on a windmilling rotor, things start moving: Imagine for a moment a feathered rotor with no engine to slow it down. If it's perfectly feathered, it won't move. If the blade angle is then reduced just a bit, the blades all start pushing air in clockwise direction, which sets the rotor in motion in anti-clockwise direction, which reduces the amount by which the air is turned again, until there is an equilibrium speed, at which the outer part of each blade is actually moving so fast that it pushes some air anti-clockwise (i.e. takes it along), while the slower-moving inner part is still pushing it clockwise. All turning angles are really small, though, and so are the resulting forces.
By comparison, a stuck rotor does not move and starts creating downwind swirl, that is: It adds some clockwise or motion to the air that's coming in, and that creates drag, of course, in the same way that a wing creating lift causes drag.
A windmilling rotor with an engine to turn is going to be somewhere in between those two cases, depending on how much torque the engine needs to be turned, and how much torque the prop is able to produce.
In this state, slowing down the prop is actually not helping!
Reducing blade angle
If we decrease the blade angle from this point, the locked propeller starts producing increasing amounts of swirl, which increases its drag about linearly with blade angle (like the lift on a wing!). Eventually, flow on parts of the blade start separating, and the force no longer increases (exactly like increasing angle of attack on a completely stalled wing also doesn't really do much).
In the meantime, a windmilling prop whose blade angle is successively reduced finds increasingly high rotation speeds at which the torque from aerodynamic forces which drive it and the ones which slow it down are in equilibrium with the torque needed to turn the engine. In the extreme case of a free-spinning prop, this will still align the blades roughly with the inflow, and cause a comparatively small axial force, since it's still just pushing some flow clockwise and some anti-clockwise. However, since there is an engine slowing things down, and higher rotation speeds require higher torque, and since the prop is spinning ever faster (higher stagnation pressure), the drag it produces does increase. Roughly quadratic with the blade angle (like the drag of a wing at increasing incidence!)
Propellers at low blade angles
And now we reach the point where the spinning rotor actually starts turning air so far that another mechanism comes into play:
When a helicopter pilot auto-rotates, they set the collective to low blade angles, and the graph above agrees that they should. The reason: the lower the blade angle, the larger the "driving" region of the blades, the more torque they develop, and the higher the aerodynamic force on the outer part of the blades, which eventually does not just add some anti-clockwise momentum to the flow, but actually turns it against the inflow direction (see Wikipedia for some details).
Effectively, the outer parts of the blades generate "lift" (that is: a resulting aerodynamic force) which has a significant component against the direction of flight: The blade profile is almost aligned with the disk plane, the rear-facing side of the blades is the suction side, and the flow on the blade is turned by almost 90°
Compared to that, the flow over the blades of a locked propeller simply separates. That leaves a big old turbulent wake behind and causes a good deal of drag, but this is way less effective at slowing down the aircraft than keeping much of the flow attached and turning it as hard as possible.
However, it should not become quite as bad as a helicopter rotor in autorotation, because the helicopter pilot is using the collective to set the blade angle such that they get close to the highest sustainable (!) force. I.e. whatever RPM gets allows them to produce the largest possible force at which the rotor can maintain its own rotation. If they relax a little, the rotor accelerates but the helicopter does, too. If they pull too much, the helicopter slows down, and shortly so does the rotor, and then the force reduces.
It would be a great coincidence if the fixed propeller on any given aircraft was installed at precisely the "optimum" pitch for autorotation. Actually, that's probably something which any propeller designer tries to stay away from.
What it means:
A windmilling fixed-pitch propeller can indeed be much worse than a non-rotating one. However, that depends a lot on the blade pitch angle (and the blade twist, because blade angle varies along the blade...), on whether it is being slowed down by the engine, and by how much...
If the blade angle is reasonably high, then trying to slow the prop down is making things worse. If blade angle is low enough to produce autorotation-like effects, then slowing it down might help (but might also be dangerous, for reasons given by others here).
How to tell what a given aircraft prefers
I don't fly aircraft, so I cannot comment on flight procedure etc., and I fully expect that proper test pilots have something to say about how easy it may be to get yourself killed (or not), but in general: For any given aircraft, the ideal glide procedure is found by turning the engine in question off and finding whatever airspeed provides the largest sustained glide number -- that is: you'd need to hold some airspeed in question until the propeller speed has settled and determine the glide angle, then repeat that for a slightly smaller airspeed, etc...
Done!

A windmilling prop is allowing the slipstream to push it around.  A stopped one is fighting the slipstream - pushing/deflecting it into a spiral.  The reaction from that is what tries to turn the plane, as Robert DiGiovanni says.  And it is doing work, because it's applying a force to the air, which moves as a result of it.
So I'd expect less drag from windmilling. Its like freewheeling on a bike versus having a locked-up wheel.
I'm assuming same AoA in both cases, i.e that stopped does not imply feathered.  Some people appear to have assumed the opposite, to which I'm curious: how would you feather a fixed pitch prop, which is what is stated in OP.

A stopped propeller is stalled and so creates a small amount of torque to "spin" the aircraft. It's drag is small as the surface blade area is small. A windmilling propeller will not stall, so the energy extracted could be much more. It depends if the prop is free-wheeling or actually turning the engine.

I would spend as long as possible trying to get the engine going again while looking for a place to land. Keeping the engine turning will maximise the chances of a restart while you try different fuel selections, mixture settings and magneto switch positions.

This does not answer the stated question. Please remember that Stack Exchange is a Question & Answer site, rather than a discussion forum. Thanks!


text:
Carbureted Rotax engines have no mixture control, how do they handle less dense air?
Rotax engines have no mixture control, yet they don't seem to have any more problems than other engines at altitude. How do they handle the lower air density in order to not get a too rich a mixture?

According to this owners manual

4.5 High altitude compensator (H.A.C. kit)
H.A.C. is a high altitude compensator developed by ROTAX which adjusts the air/  fuel
mixture automatically from sea level to 6500 m altitude using a
special BING  carburetor.

This page has information on how the Bing carburetor works (with pictures!):

Here's how it works
Did you ever wonder what makes fuel flow up the jets, from the
carburetor float bowl, enroute to the engine? Is it vacuum at the
venturi?  That's not quite descriptive enough. It is better defined as
a differential pressure between the float bowl and the venturi. What's
the pressure in the float bowl? Here is an important hint, the bowl is
vented to outside atmosphere. So, it should be the same atmosphere, or
ambient pressure, that's feeding the airfilter.  If it is not,  the
differential between the venturi and float bowl is going to change and
so will the mixture...Maybe richer, maybe leaner. Just think of that
for a second. If  fuel air mixture can be thrown off, accidentally by
improperly venting the the float bowls, why not control the venting to
effectively control mixture? That's exactly what your Bing 54 can do,
automatically, when a High Altitude Compensator is added.  If
pressure in the float bowl is reduced, relative to the venturi,  less
fuel makes its way up the jets, and consequently, mixture is leaner.
The HAC unit has two chambers separated by a diaphragm. One chamber is
completely sealed (except during calibration) and air density within
remains constant. The other has airfilter, float bowl, and venturi
connections, so air density on this side is variable. It is in this
chamber, that ambient pressure can be reduced by feeding it to the
venturi via a connection on late model carburetors. The amount of
ambient reduction is controlled by a tapered needle which changes
position with deflection of the diaphragm. Think of the diaphragm as a
flexible wall between two chambers that allows the sealed side to
expand or contract as changes in ambient pressure occur on the other
side. The reduced  (from ambient) pressure gets routed to the float
bowl(s) via their vent lines with a resulting leaning affect..  If
that supply of low pressure is shut off, float bowl pressure returns
to ambient, and the mixture goes as rich as the jets will allow. With
HAC installations, standard jetting starts out several steps richer.
This is why we say the default, or failure mode is typically toward
the rich side.

The simple answer to this, is that Rotax employs Constant Depression carburetors, which is a type of Variable-Venturi carburetor. In essence the fuel/air ratio is adjusted automatically based on air pressure.
The fuel jet opening is varied by a tapered needles that slides inside the fuel jet and is controlled by a vacuum operated piston.

Some new Rotax engines, such as the 912 iS, are fuel-injected and include a Full Authority Digital Engine Control (FADEC):

FADEC works by receiving multiple input variables of the current
  flight condition including air density, throttle lever position,
  engine temperatures, engine pressures, and many other parameters. The
  inputs are received by the EEC and analyzed up to 70 times per second.
  Engine operating parameters such as fuel flow, stator vane position,
  bleed valve position, and others are computed from this data and
  applied as appropriate.

source: Stack Exchange

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sort: votes


text:
How do planes on taxiway get back to terminal after an accident?
When there is accident that blocks the runway, how do other planes that are on taxiways or holding points move back to terminal? After all, the runway is closed due to the accident and planes cannot just reverse back to gate.

A runway may be technically closed, but in an emergency some of it may still be passable for taxi traffic under ATC control.
For example at Haneda:

Source:Wikimedia Commons
Runway 34R/16L at Haneda has two parallel taxiways. Any aircraft on those taxiways can simply taxi ahead to a turning point and follow ground control directions to a gate.
After the accident Runway 34R was technically closed, but any aircraft holding for take off near the threshold could taxi onto the runway, proceed to the next exit point, and exit the runway again, all under ATC control, obviously.
If that's not possible then they could enter the runway, backtrack and exit at the next entry point.
For any aircraft for which these options are not feasible, they can sit tight and await the services of a tug.

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text:
Can a PPL be a safety pilot?
I got a question from PPL oral checker, but I was not able to answer. The question:

If a pilot is practicing an instrument approach in VMC, can you be a safety pilot?

I've added the FAA regulations tag, since you've accepted an answer based on 91.109. If you're asking questions about regulations, please always tell us which country or regulator you're interested in.


text:
When should ATC terminate radar service to VFR aircraft?
According to FAA order 7110.65AA 7-6-11,
"Basic radar services should be provided to the extent possible, workload permitting. Terminate radar service to aircraft landing at airports other than those where sequencing service is provided at a sufficient distance from the airport to permit the pilot to change to the appropriate frequency for traffic and airport information."
If sequencing service is provided at a sufficient distance from the airport, when should ATC terminate radar service? I wonder why there is an exception in paragragh 7-6-11.

The intention of that paragraph is to give the pilot enough time to safely communicate their intentions and perform the necessary coordination at the landing airport. This may be a Class D airport where Tower provides the sequencing services, or it may be a non-towered airport where the pilots sequence themselves on CTAF.
For a towered airport the "Transfer of Communications Point" will be specified in the Letter of Agreement between the Tower and Approach facilities. Six or seven miles from the airport is a common minimum.
For a non-towered airport there will be no formal Letter of Agreement so it comes down to technique on the part of the controller. I consider it very poor service to hold on to a pilot inside of five miles from the field; unless I get distracted by something else I will generally terminate services and let them change to CTAF at around ten miles.
Of course the pilot may request a frequency change at any time.

If sequencing service is provided (by Approach) then the Transfer of Communications Point is the required point at which communications should be transferred. This may or may not be a "termination of radar services." Some Tower facilities have the requisite equipment and training to provide radar services themselves; at other towered airports the Approach controller will specifically say "radar services terminated, contact Tower." See 5–1–9b3.


text:
Why did this flight, that usually flies around 40,000ft only fly at around 29,000ft for the route?
Looking at the flight BY6272 BRS-PMI, it was considerably delayed and flew (according to the flight radar app) at 29,000 feet rather than its usual 40,000 for this same route. It is a Boeing 787 Dreamliner. Flight time is usually around an average of 2hours.
This flight is weekly. Why would it fly low on some weeks and high on others?
July 12, 2022:
June 28, 2022:

It sounds as though the airplane was not RVSM capable for some unknown system failure.

RVSM starts at 290.  If you're non RVSM, you're stuck below that.

I’d be hard-pressed to think this is an RVSM issue considering A/C in question is a B-787.  It would seem this is more up to the individual airlines flight planning dept. for routing weather, scheduling, etc.

Just spitballing... is 290 a limit for any MEL's on the 787?  Like pressurization, maybe? (Flying with 1 pack deferred on the 737 limits us to 250; dunno if the Dreamliner might have a slightly higher limit due to differences in their systems.)

Failure of the one of the ADC systems will preclude flight inside RVSM airspace.  Part 91 appendix G has other equipment that will preclude flight inside that airspace.  If the flight was originally cleared higher but then decided to stay at FL290, a failure like this is the most likely cause.

@757toga.  I would agree with you.  ATC can suspend RVSM separation at any altitude.  I would imagine ATC allowed the airplane to be there at the lowest altitude.  No one here really knows why the flight was flown so low.  It is all speculation.

Do we know winds aloft or other weather factor?  Possibly a speed benefit (looks like it was going faster) to make up for the delay that was mentioned?

@757toga I agree that the image in the question for 12 July (added by tedder42) is wrong (probably from another date). However, on 5 July the flight climbed to FL430. It's perfectly obvious that FL290 is well below any reasonable cruise altitude for a 787, regardless of what the typical cruise altitude of this flight is. Voting to leave open.


text:
Can a formation flight operate in class B if only the lead aircraft is equipped with a transponder?
We all know that you can't fly in Class B airspace without a transponder. But, when doing a formation flight, only the lead plane has their transponder turned on. Does that mean that it's possible for a non-transponder-equipped airplane to fly through Class B airspace so long as they're part of a formation flight?
If so, would they need to arrange it ahead of time with the ATC facility, or could they just notify ATC when they're requesting entry to the Class B, or do they not need to even tell ATC that one of their planes doesn't have a transponder (not saying that the last option is a good idea, just asking if it's legal).

Closely related, but doesn't address the question of aircraft that don't have a transponder

Would you be VFR, or IFR in IMC?  One time flight, or plan to operate that way regularly?


text:
Why don't combat aircraft have rear-facing *laser* weapons?
This question is similar, but only talks about guns. I don't mean a laser that is going to destroy the plane, but why aren't rear-mounted, rear-firing lasers that can blind a pilot a thing? Most of the concerns about weight and relative velocities from the other question disappear with a lighter-weight laser that is firing light.

Infrared countermeasure (https://en.wikipedia.org/wiki/Infrared_countermeasure) or Directional Infrared Counter Measures (https://en.wikipedia.org/wiki/Directional_Infrared_Counter_Measures) .

Sharks with frickin' lasers on their heads. Ummm... Planes with frickin' lasers on their tails!

If you ask a similar question on Worldbuilding, phrased different enough as to not be a cross posting (such as "what would be required for a laser..."), you'll get a very different set of answers.

Temporarily blinding with laser might be doable, no matter conventions and whatnot. But what have you achieved by that? Pilot will close his eyes and send you a missile. And hope his eyesight recovers in time to land. Next flight, all will use laser goggles.

@ZizyArcher laser glasses for what wavelength? You can build lasers for any visible light, and the only way to block those would be completely opaque.  Don't think about auto-darkening stuff; one tunable laser I've got here could burn a hole in your retina in a nanosecond, and the other could dazzle you if not worse in a few picoseconds (the latter is a bit big, the former is the size of a suitcase).

Air-to-air dog-fighting combat a la Top Gun basically doesn't exist anymore.  Most of it is done with guided missiles from far beyond visual sight-range, so a laser to blind the pilot behind you would be of limited use.  By the time they're close enough for that to be effective, they could've easily shot you out of the sky several times before you even knew they were there.

@J..., actually it's not that simple. This is what I do for a living. The ns laser I mentioned tunes in 0.1nm steps across the entire visible range. In one go, with enough power that a single pulse hitting your windscreen would dazzle you, and directly hitting your retina would leave a blind spot. That's not even optimised for this job (it's an OPG pumped by the third harmonic of a Nd:YAG, for any other laser scientists reading this). The best countermeasure would be a blacked out cockpit, flown by screen, but the cameras probably wouldn't like it either.

But I'd actually use around 3 discrete lines, so that any reasonable blocking glass would block a lot of visible light. Seeing what's going on adding you is already hard with goggles to block up to 532nm (a high power green line) as everything goes orange. Add the need to block red and things get even harder. Narrow band blocking is only possible for small ranges of angles, and tends to cause interesting artefacts as the angle changes.

@J... With military money it would be a matter of wanting it enough. Those single wavelength 1st generation systems could have been built 20 years ago (related systems for use on the ground were being investigated in the 90s and the main problem was power, otherwise they would lie have been man-portable). So with military backing the tech could be flying. You can get the harmonic for free when designing a narrowband blocker (e.g. holographic notch filters). Multi-bandpass is interesting but will be limiting in low light. Other reasons dominate - like attracting attention, and legality.

@J... If they're commercial I'd be interested. It's normally the shift with angle that's the issue in work though.

@J... Definitely worth a look in work (I'm a sort of deputy LSO as well as a researcher). I didn't know Iridian made glasses, but it's probably 10 years since I bought Raman filters from them

@J... I suspect that's a major part of the difference in our views. Also IIRC lab laser glasses have some other fairly tight requirements that may be hard to meet with a reflective blocker

Whatever the reason for not having them... there is a reason, and it's not because of Air Force stupidity.

Because you need a 747 to put a weaponized laser into the air, and it "would need a laser something like 20 to 30 times more powerful than the chemical laser in the plane right now". Boeing_YAL-1. Status: canceled.

Such weapons are not used by countries that abide by the Geneva Convention:

It is prohibited to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision, that is to the naked eye or to the eye with corrective eyesight devices.

For the U.S.A., page 45 of Navy Shipboard Lasers for Surface, Air, and Missile Defense says:

Hmmm. .... is that really the REASON they are not used?

@quietflyer it's one reason. Another reason is power requirements.

The convention, power requirements, limited usability, lasers being awfully hard to target and the collateral damage of missing the target, there's a lot of reasons not to do this. It's generally more useful to shoot an enemy bird out of the sky than turn it erratic by blinding the personnel.

@quietflyer Remember what chemical weapons caused to their survivors in WW1. No-one wants thousands or more blind laser-weapons survivors. And remember, even if you are in a technically advanced country currently mostly fighting developing countries or insurgents with little technology, next time your soldiers maybe those that return home blind.

@jwenting power considerations used to be an issue.  Modern solid state lasers are much smaller, lighter, and more efficient.  Scanning a small cone pointed in roughly the right direction could be done in a kilowatt (power consumption), with enough beam power to draw permanent stripes inside your eyes.  A 10kW system would be doable and have much more chance of hitting, either to permanently blind or to dazzle, depending on range and how divergent you make the beam

@VladimirF: So it's better for thousands to return home in body bags than return home blind?

@R, Taken literally, yes, hundreds of countries have said so.  Obviously the issue isn't that simple, and it's also beyond the scope of Aviation SE.

@CamilleGoudeseune Yes, it's about banning "unfair" wartime practices. In peacetime, everything is OK: “The Geneva Convention declared tear gas to be a form of chemical warfare, and it is banned in such conflicts.  However, it is not banned in civilian situations, either by individual use of pepper spray, nor by law enforcement use in the form of tear gas.”

@cyco130: That's one of the problems the US had/have in e.g. Iraq and Afghanistan. By insisting on declaring everything a "war" (war on drugs, war on terror, etc.) and using soldiers for everything, they limit their options in peacekeeping. A soldier policing a crowd can only kill them, a police officer can use tear gas, tasers, water cannons, rubber bullets, noise weapons, etc.

@R..: Yes, more or less. The basic idea of The Hague Convention, Geneva Convention and related Treaties is that soldiers are allowed to use weapons that are designed to kill individuals against other soldiers, and that's it. They are not allowed to use weapons against non-combatants, they are not allowed to use weapons that are not directed at individuals (WMDs, basically), and they are not allowed to use weapons that are designed to maim, or injure. This means that the entire arsenal of sub-lethal weapons that are available to police officers are off-limits for soldiers.

looks at techniques and weapons used in Guantanamo, Syria, Yemen, Afghanistan, Ukraine, Gaza. okay, what's the real reason?

I don't think this is really the answer, due to the part about "permanent blindness".  Temporarily blinding an enemy pilot would still be both (theoretically) useful and in-bounds under the Geneva Convention.

@aroth assuming you can control it precisely enough for that. Ask anyone who deals in distance weapons, it is very hard to control severity of damage.

Besides the other answers, international law and the technical complexity of putting a laser on an airframe, lasers have interesting limitations as weapons. Lasers do not deal well with cloud cover. Hundreds of meters of cloud cover between two planes flying on instruments disrupts a laser's coherency, but not a guided missile's accuracy. After passing through a significant amount of cloud vapor, the laser will not have enough energy to damage the target or blind the pilot. You can imagine how unappealing spending money on a weapons system that is made useless by clouds is.
Another factor is that modern air combat is rarely 1 plane vs 1 plane. Ground radar, AWACS planes, satellites, and allied aircraft all work together. It does you no good to blind a single opponent if ground radar has locked on to you, because modern systems can pass that lock to missile launchers and other aircraft. Now anyone in range can launch a guided missile at you, a guided missile you can't blind.
As more airplanes become drone piloted, blinding the drone's cameras  will not stop the operator from retaliating against you, because the drone's radar and other instruments are still functional.
So why spend money to solve a problem that is only tangentially related to your real problem? The problem is not that another pilot is in the sky. The problem is them being able to lock on to you with guided missiles, or even know you are around. If you have technology that prevents their missiles from acquiring an accurate lock, launching missiles is just a waste of money.

The Geneva Convention only addresses permanent blinding. Temporary blinding is all it would take to render an enemy pilot unable to react for at least long enough for you to employ evasive maneuvers and/or come around for an offensive. That said, one wouldn't even need a laser. Any sufficiently bright LED array would do the job.
Of course, this assumes the enemy pilot isn't equipped with any kind of eye protection.

It would need to be extremely bright, modern engagements happen over distances of several kilometers.  But it is technically possible.

Other than the minor statement in the last sentence this doesn't seem to answer the question.

That would be the instant retort of the adversary, a filter on their goggles or cockpit window.

In addition to the already mentioned Geneva convention, there is also the power requirements issue.
Lasers powerful enough for combat weapons require more electrical power than can be generated by a fighter (one reason why the YAL-1 was based on a Boeing 747).
Also, high power lasers generate a lot of heat.  Heat dispersal in a small airframe is difficult, especially if you want to minimize your IR signature.

Is there a reason to believe that the power or space requirements for the YAL-1, designed to intercept ICBMs during their boost phase, would be comparable to the requirements for a laser designed to illegally blind enemy pilots who are presumably in a dogfight with you?

That really depends what you mean by combat weapon. Will it cut through the plane's hull? Doubtful, that indeed requires a lot of energy. But there are enough accounts of idiots blinding pilots with a laser pointer from their home. It only takes 1W to cause serious damage.

You can buy a laser pointer that can blind an airline pilot on Ebay for less than $50 that runs off of AA batteries

There's a difference between "oops, we accidentally broke the Geneva Convention because we couldn't keep our weapon on target long enough to kill the pilot instead of just maim them wink" and "this weapon can only be used to violate the Geneva Convention." -- To have a blinding laser without immediate sanctions, such a weapon system would have to be plausible as an anti-vehicle weapon as well, hence the very high energy requirements. (Though heat dispersal isn't as much of an issue as implied. If you can deal with jet exhaust, you can deal with a laser weapon.)

@Ghedipunk Doesn't have to be anti-vehicle. A cover story could just be that it's intended to burn out the sensitive IR sensors in an incoming missile.

@ceejayoz How do you target a missile?

@curiousguy Same way you'd target any other small flying object. Radar, visual tracking, etc. Laser dazzlers for inbound missiles already exist: https://en.wikipedia.org/wiki/Shtora-1 So do anti-mortar interceptors: https://en.wikipedia.org/wiki/Counter_Rocket,_Artillery,_and_Mortar

@ceejayoz I thought even small planes (and missiles) were never targeted so precisely they would be hit right in the nose.

@curiousguy It's easier to point a laser at something than it is to hit it with something physical. Adjustments are instant. Missiles will have proximity fuses to increase the chance of a kill via shrapnel, but we've had long had laser designators that can lock on and track small moving objects.

What about the visual interference generated by the jet exhaust?

@ErinAnne: No, there is no reason to believe that, especially since it isn't true. The power needed for a laser weapon that can blind a pilot over a reasonable distance is well within any military plane's power budget.

Because weapons of mass destruction are maintained and developed, the Geneva Convention might not be respected much during wartime.
Also, F-35s and F-22s have been mentioned in articles proposing laser weapons systems:
https://nationalinterest.org/blog/buzz/f-35s-and-f-22s-could-soon-fire-laser-weapons-think-laser-dogfights-83586
https://www.militaryaerospace.com/power/article/14034450/laser-weapons-jet-fighters-unlimited-magazines
If ignoring the Geneva Convention, I'm not sure how effective such a weapons system would be. Wouldn't it be rather trivial to mitigate most or all of the damage by the enemy pilot, once such an imagined laser system is known to be used? The pilot would merely need to wear protective laser goggles or use other means of limiting the amount of light that enters the eye. The cost of developing the laser weapons system, compared with cost of the protection against it (laser goggles) doesn't seem to add up.
Also, an aircraft that sends out a continuous hundreds-of-kilowatt laser beam towards your own sensors provides an attractive target for your own  missile.
You might impair the other pilot's visual flight when the beam is on, but looking down at the instruments to fire a missile should be possible when sufficient eye laser protection is worn.

A laser beam in the range of hundreds of kilowatts of continuous power is far beyond blinding.  Solar irradiance is in the realm of 1.4kW/m^2 and unmitigated direct sun exposure is already a problem for many kinds of sensors; the kinds of mitigations you can take to prevent those sensors from being blinded outright go on to impact the sensors' ability to detect things that aren't as bright.

authors: Vladimir F Героям слава


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Would a laser dazzler be militarily useful?
I saw Why don't combat aircraft have rear-facing *laser* weapons? pop up in the Hot Questions list and that motivated me to join here and ask this question.
Weapons that blind are banned. But what if they merely dazzle?
I'm imagining a little box with a laser pen in it - like those that so trouble landing pilots when wielded by foolish people on the ground. The box can point the laser around the sky and switch it on or off. It's a relatively cheap unit. It's probably controlled from an air defence computer that is looking at radar, IFF etc, that tells it where to point. If a hostile aircraft arrives, dazzle it.
Of course, the first thing the hostile aircraft will do is shoot up the box. (So you wouldn't want to be a human defender pointing a laser pen.) But if the boxes are cheap enough, you could scatter a hundred or so around any base you were trying to defend, and target an attacker with just one box at a time. When it gets blown up, use another box.
Without fancy radar, IFF etc (you may have no aircraft so you want to dazzle all of them) you could put a camera and image recogniser in each box.
If it all goes wrong and points at a friendly aircraft or even a human on the ground, probably no harm will come. But it seems it would make it much harder for an aircraft flown by a human to attack a target. It could work against drones, too, even relatively high-flying ones.
Would it work?
Would such a system be legal? Practical? Has anyone deployed one? Is anyone working on one?

Such a system already exists (in a way) and is in place to warn pilots who improperly enter the DC SFRA area. Im not sure it "dazzles" but it is what you describe and could be extended to do so. You can see an example of it running here.


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Can a paraglider rescue chute and its pilot handle terminal velocity?
Imagine a paraglider cuts his main chute and reaches terminal velocity. Can he still land safely when he deploys hes rescue chute?
The european standards require that paragliding rescue chutes can handle opening shocks as high as 60 m/s at full load. Google tells me that termial velocity is around 53 m/s for a human skydiver. Is that requirement enough to safely say it can handle terminal velocity? Note that a paraglider can have equipment up to 15kg. Is it possible one could hurt himself when opening paraglider rescue chute because they can open to fast?
European Standard EN12491
EDIT: I've found this post where somebody talks about how he deployed a hangglider reserve while he was falling at terminal velocity. He talks about how he survived and how he has seen another similar case where it went the other way.

The EDIT link is talking about a hang glider incident, I'd expect their reserves to be a lot more sturdy than a paraglider's

Just a note on terminal velocity: the 53m/s quoted is for a (trained) skydiver falling belly to earth, arms and legs spread out, and stable (not tumbling or spinning). The most difficult thing to teach beginning skydivers is how to get stable and stay that way. If you're not stable you terminal velocity will be rather higher. Speed competition have been held which reach, IIRC, 90m/s - but a beginner probably wouldn't be able reach and hold that. so a tumbling freefaller (which is likely without specific training) will have a terminal velocity of over 53m/w but less than 90.

I have been told in person by the owner of High Energy Sports, a well-known manufacturer of hang gliding / paragliding emergency parachutes, that their products are not designed to be safely deployed at the terminal velocity of a falling human being.  Regardless of what some particular standard might suggest, I doubt that any hang gliding or paragliding emergency parachute is really designed to have a robust safety factor in the context of deployment in a true terminal-velocity freefall.  The greatest concern would seem to be catastrophic failure of the parachute and/or harness, not injury to the user due to opening shock, but the latter would seem likely to be a possibility as well.
Keep in mind that a hang glider or paraglider pilot does not actually cut away from the rest of their equipment (e.g. the main canopy of a paraglider) before deploying their emergency parachute.  There is no way to easily do so.  And that is why the reserve parachute is not designed for a terminal velocity freefall.  (Edit: see other answer for an exception-- apparently some paragliding rigs are designed to allow for a cutaway.)
Nonetheless, in an article in "Hang Gliding" magazine from well over ten years ago, well-known test pilot Mark Stucky described an incident from his younger days when he went skydiving using his hang gliding emergency parachute.  I don't recall whether the article specified how long he waited before opening the parachute and whether or not he might have been anywhere near the maximum terminal velocity of a falling human being-- one would tend to assume not.  He did survive without injury.
See also answers to related question Whats the difference between a paragliding rescue chute and a parachute?

Maybe another answer will include links to information from the industry; I suspect a simple google search would turn up such information. Those links could be added to this answer.

If my main chute fails and I need to use my emergency, I'm not sure I'll care that I'm "over speed", the possibility it may work much outweighs reserving yourself to it not and hitting the ground at full speed.

I have to disagree with "Keep in mind that a hang glider or paraglider pilot does not actually cut away from the rest of their equipment". There is equipment especially designed for this purpose but it is only done on special occasions. And it is being discussed if it is the best option in case of "cloud suck" (When you get sucked to the stratosphere). I've also found this acro equipment which does not contain paragliding rescue chutes but parachutes. But thanks a lot for your answer.

I agree with @NtFreX. There is such way ("Quick release carabiners") but afaik it's not considered a civic way to handle an emergency situation (implies that canopies may be lost in nature) and isn't widely used.
It looks like this :
https://www.paragliding.com/shop/accessories/carabiners/finsterwalder-quick-release-carabiner-pair/

There isn't an easy way to 'cut the main' on most paragliders  The risers are attached to the harness by maillons and as long as the wing is doing something, they are under tension and difficult to unclip.  Also, the reserve is attached to the harness, not directly to the pilot.  The whole lot should come down together.  One exception to this is a cut-away system that some acro pilots use, when they pull their reserve the wing detatches and deploys the reserve as it goes.
What usually happens is that the wing stops flying, for whatever reason, and if the pilot decides that he/she can't get it working again they will throw their reserve.  They will be falling at this point, but since they started from close to zero sink and there is a lot of drag (not enough for a safe landing) from the wing, at the time the reserve is thrown they will be nowhere near terminal velocity. The main problem then is to prevent the wing interfering with the reserve so it should be pulled in and kept out of the way.  This page describes the process and there are some 'interesting' videos of what actually happens.
Paraglider reserves are very different from skydiving reserves.  The latter are deployed at terminal velocity (or close to it) and have stronger lines and attachments.
I think I'm right in saying that landing on a reserve is never easy (I've never done it).  You have less control over where to land and you will come in faster than otherwise.  Reserves tend to be small and light to keep weight down.


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What is nominal n1 and fuel flow behavior during cruise climb?
For a commuter airliner (e.g. 737) performing a cruise climb (step climb) at a constant Mach, how should n1 and fuel flow behave?
I know that fuel flow should decrease with altitude (air fuel ratio).
Should fuel flow also decrease with weight (fuel burn off)?
Is n1 kept constant? Does it decrease with weight? Is it unaffected by altitude?
If it depends, then what systems (fadec?) or settings (rated/non-rated mode?) are responsible for setting the behavior.

Where did you get the data? What type of aircraft/engine?

homework, Commuter Airline, exact aircraft/engine not specified

I'm voting to close this question as off-topic because it is a homework question.

Ralph - I have rewritten the question and removed the graphs to make it non-homework specific (removing many of my own questions). It is a question of basic understanding and hard to find definitive answers online.

I know that fuel flow should decrease with altitude (air fuel ratio). Should fuel flow also decrease with weight (fuel burn off)?

Yes, the lighter you are the less N1 you need to maintain the cruise Mach at your cruise altitude. This will result in a lower fuel flow (at fixed environmental conditions, lower N1 always results in lower fuel flow).
The maximum climb N1 is however independent of weight (see below for details), therefore also fuel flow will be independent of weight during climb (but the resulting climb rate is different).

Is n1 kept constant? Does it decrease with weight? Is it unaffected by altitude?

The cruise N1 depends on both weight and altitude. The following table from the 737 NG QRH (Performance Inflight - Flight With Unreliable Airspeed) shows the target N1 values for various weights and altitudes:

As you can see, N1 goes up with weight and up with altitude. The maximum climb N1 has a more complicated behavior as function of altitude, as the following table from the 737 FCOMv1 (Performance Inflight - General) shows:

The last 3 columns all show climb at fixed Mach 0.78. The N1 usually goes up with altitude, but then slightly down again for the highest altitudes (this is because TAT goes down with altitude up to the tropopause, but stays constant above). The maximum climb N1 is independent of weight, but the actual weight will affect the resulting climb rate.

If it depends, then what systems (fadec?) or settings (rated/non-rated mode?) are responsible for setting the behavior.

For the Boeing 737, the required fuel flow to reach the target N1 is computed by the EEC (Electronic Engine Control, see also What are the differences between FADEC and EEC systems?). From the 737 NG FCOMv2 (7.20.5 Engine System Description):

Electronic Engine Control (EEC)
Each engine has a full authority digital EEC. Each EEC has two independent
  control channels, with automatic channel transfer if the operating channel fails.
  With each engine start or start attempt, the EEC alternates between control
  channels. The EEC uses thrust lever inputs to automatically control forward and
  reverse thrust. N1 is used by the EEC to set thrust in two control modes: normal
  and alternate. Manual selection of the control mode can be made with the EEC
  switches on engine panel.

The target N1 calculations are performed by the Flight Management Computer, but can be overridden by the pilot. From the FCOMv2 (11.32.2 Flight Management):

Thrust Management
The autothrottle operates in response to flight crew mode control panel inputs or
  to automatic FMC commands. Reference thrust can be selected on the N1 LIMIT
  page. Automatic FMC autothrottle commands are made while VNAV is engaged.
  The autothrottle system:

And further (11.41.28 FMC Takeoff and Climb):

N1 Limit Page
[...]
Normally, N1 limits are automatically specified. Pilot selection of other limits is allowed.
Pilot selection of a reduced climb mode does not change the automatic selection
  for other phases of flight.
Pilot selected mode is automatically replaced by AUTO selection when the
  autopilot next changes vertical mode.
The active thrust limit is used by the autopilot and is displayed on the thrust mode
  display.


text:
Can thrust vectoring be used to enable the use of flaps on tailless delta-winged aircraft?
I'm considering flying wings as well as airplanes with only vertical stabilizer for their compact size, efficiency and high speed.
As I can't find a working example of such scheme, theoretical explanation is very welcome.
To compensate for rear end additional lift, thrust output will probably be placed at the nose.
Possible options by propulsion types:
Propeller

tilted prop rotor (fixed / variable pitch)
propwash forwarding - canard fins
collective pitch thrust vectoring (swashplate driven)

Jet

additional small engine at the front (electric ducted fan)
ducts from the main engine
fan driven by the front shaft of the engine (as in Harrier Jump Jet)
tractor placement (as in ekranoplan)

Problems
(summary from answers and comments, thanks for valuable input)
Stability.
Change of angle of attack either intentional or by air conditions changes wing lengthwise distribution of lift.
Is it manageable for human to safely maintain stability in such conditions and if not - for a computer?
Thrust availability.
Approaching landing the forward thrust is minimized, so there should be close to 90° downward thrust line deflection.
Thrust agility.
Combustion jets are sluggish. There should be a nozzle limiting the output.
Partial reverser?
Safety.
Engine out below unpowered stall-speed at landing sounds like a nose down crash.
Redundancy should help.
So, is it viable to add enough nose-up moment and stability by vectoring thrust to counter the nose-down moment produced by flap extension, thus allowing STOL capabilities with flaps at acceptable angle of attack?

Practical implementation discussion https://www.homebuiltairplanes.com/forums/threads/can-thrust-vectoring-enable-use-of-flaps-on-pure-delta-wing.32781/

No, for several reasons
What you want is to compensate for the additional lift from downward deflected flaps at the back of a flying wing with vectored thrust. As @Sean points out this will not bring a noticeable net benefit if the lengthwise location of both forces is similar.
But that is not all.
Besides the force equilibrium around the flying wing you also need to consider how it behaves when flight parameters change, say by gusts. Will it return to the old state? How will the dynamic behavior be?
More camber means that the zero lift angle of attack becomes more negative. A deflected flap adds camber near the trailing edge. If the wing now assumes a higher angle of attack due to a gust, the change in local lift over chord will make the wing pitch up more. The forward region of the airfoil will add more lift relative to the initial state than the rear region because the zero lift angle of attack has been shifted downwards, adding a pitch-up moment. The whole aircraft will become unstable from the added camber of the flap.
Flying wings don't need computer control. All the Hortens and Fauvels of this world flew just fine with a human pilot and mechanical controls. That is because they use reflex airfoils and wing twist so the rear part of the wing creates less lift relative to its area. This is the condition for static stability and it gets removed with a positive flap deflection.
Adding that flap will add so much instability that computer control would have a hard time to keep the aircraft stable. If the flap produces substantial additional lift, the thrust vector control would need to effect large changes in pitching moment. Now consider you fly into an airport along the glide slope, with the engine close to idle. Where would the required pitching moment come from? Thrust is insufficient and reducing your flap setting will stall the aircraft. The best solution is to not deflect the flap in the first place and to add more wing area relative to a conventional aircraft.

if by "stability" here you mean even lengthwise lift distribution in all conditions (with extended flaps), than this is exactly what I'm trying to cope with computer.
Regarding the glide slope: just point the thrust vector down, so it would produce no horizontal force.
Why do you think it is not possible with sufficiently responsive thrust vectoring?

@Anbu It takes time for thrust to ramp up, especially for jet engines near approach idle. Even then, it messes up the glideslope control due to rapid thrust changes.

most jet engines are sluggish, but there are other options like: tilted rotor or collective pitch thrust vectoring. Even jet thrust may be controlled rapidly by converging-diverging nozzle.

@Anbu Most jets are sluggish. They are even more sluggish near approach idle, that's what we are trying to say here. I don't see how converging-diverging nozzles help; if your N1 is spinning slowly, it takes time to ramp up.

Nozzles of variable area can control the gases exhaust speed by changing shape.  Not sure about the range, though. Keeping higher rpm the engine will produce less thrust, while quick nozzle response will substitute the slow change of engine rpm. Besides, while the engine is working partially to lift the nose up it will already be under some load.

@AnbuAgarwal: If the exit impulse is low, the area of the nozzle will not magically provide more control authority. Changing the exit area only improves efficiency.

@peter-kämpf, thanks for explanation, I understand that variable nozzle area may be a bad idea, but what do you think of dynamically tilting rotor which would definitely have enough responsiveness with blades variable pitch?

No.
Thrust vectoring produces a nose-up pitching moment by pointing the engine nozzle upwards, which pushes the aircraft's tail down and its nose up.  Extended flaps increase total lift, and produce a nose-down pitching moment, by deflecting air downwards at the trailing edges of the wings, pushing the aircraft's tail up and its nose down.
As the engine nozzle(s) of most delta-winged aircraft are at about the same distance from the aircraft's center of mass as its elevons (flapevons?) are (both being either at, or very near, the rear end of the aircraft), the use of thrust vectoring to cancel out the nose-down pitching moment created by flap extension would require that the deflected engine nozzle apply a downforce (anti-lift) with approximately the same magnitude as the upforce (lift) applied by the extended flaps - completely (or almost completely) cancelling out the increase in lift produced by said flaps!1
Aircraft with a horizontal tail (including most non-delta-winged aircraft as well as a number of delta-winged aircraft) don't have this problem, as the elevators are at the far posterior end of the aircraft, far from its center of mass, while the flaps are mounted on the wings, very close to the aircraft's center of mass; thus, a small amount of downforce from the elevators produces enough nose-up pitching moment to completely compensate for the nose-down pitching moment produced by even a very large amount of flap-extension-produced lift.2  Canard aircraft (including some non-delta-winged aircraft, and also some delta-winged aircraft) don't have this problem, as the nose-down pitching moment from extending flaps on the main wing can be cancelled out by the nose-up pitching moment from extending flaps on the canard, which has the additional advantage of increasing the aircraft's lift coefficient yet further (instead of slightly decreasing it, as the nose-up elevator deflection required when the flaps are extended on most horizontal-tailed aircraft does).

1: If the nozzle(s) extend rearwards beyond the trailing edge of the wing, then they would have a slightly longer lever arm than the flapevons, allowing a slightly lower amount of vectored-thrust downforce and a small increase in lift with flap extension, but the additional lift gained thereby would likely not be enough to be worth the trouble.
2: In practice, this is an oversimplification; for some horizontal-tailed aircraft, extending the flaps actually produces a nose-up pitching moment.  However, this is due to the interaction of the wing's downwash with the horizontal tail (and, thus, would not be the case for a tailless-delta-configuration aircraft), and the point about the elevators' much longer lever arm compared to the flaps is still valid.

having thrust output near the flaps will obviously not work, but what about having it near the nose?

@AnbuAgarwal: No, because the engines are in the back, near the flaps.

I understand that your refer to the majority of jet delta-winged aircraft but there are other options: nozzles placed away from the rear end, tilted rotor or collective pitch thrust vectoring and probably some other I'm not aware of.
I'm asking about the viability of proposed scheme even if it was never tried.

Yes, but it may not be worth it.
In principle it is absolutely possible to use thrust for attitude control of a vehicle. To cite a few examples, the F-35, X-15, and Harrier all used ducted jet exhaust or high-pressure bleed air for attitude control during low dynamic pressure phases of flight.
You correctly point out in the question that the thrust would have to be at the nose (not normally where you want your engine) and inclined so the thrust line is 90 degrees downward.
So another way to ask this question would be "can you replace a canard on a delta-winged aircraft with a vertically thrusting engine"? In principle, yes. Is it a good idea? Probably not. But how good or bad of an idea it is depends on several factors. Some of the challenges have already been mentioned so I won't repeat them here, but other things to consider are:
1) How far the nose is from the C.G. Your concept makes more sense if you have a long nose on the airplane (think XB-70). For a pure flying wing you would need a lot more thrust to achieve the same pitching moment since the moment arm from the thrust location to the C.G. would be as small or smaller than the moment arm from the flap to the C.G.
2) The type of propulsion system used Tailless aircraft are very sensitive to C.G. location, so if you add a lot of weight to the nose that will make the aircraft difficult to balance.  For that reason, it's more advantageous to use lightweight secondary propulsion systems (ducted exhaust from a turbine).  Putting a large electric fan or secondary turbine in the nose will add weight in a difficult place to balance. There is a trade here with the benefit you get from a longer nose - you'd have to actually work it out for your design to see if there's an option that makes sense.
3) Pitching moment variation with speed
Dynamic stability (include gust response, pilot handling characteristics, etc.) is going to be a challenge for this type of plane in general. But it's a solvable problem; whether its solvable with a computer in the loop or not depends on some of the other details of the design, but flying wings, canard aircraft, and delta wings have all been built which require little or no stability augmentation.
There is one big stability challenge that this concept brings with it, which is that the effective pitch-up moment you get from the thruster will change relative to the flap pitch-down moment as speed varies.
Typically you'd calculate the trim condition of the vehicle in terms of key dimensionless parameters like $C_{L_\mathrm{tail}}$ and $C_{m_\mathrm{wing}}$, and when the aircraft is in a trim state the variations in these parameters with speed are very small; so small changes in speed won't effect the trim condition of the aircraft.
If you're using a thruster to generate your pitching moment the force of the thruster is dependent almost entirely on the jet velocity of the thruster, and almost totally independent of the freestream (especially in this case where it's oriented 90 degrees). This means that, as your speed changes, you'd need to constantly be modulating the thruster input to keep the right pitch trim. Since unlike other reaction control aircraft your thruster will always be on, keeping it at the right power setting will at best add significantly to the pilot workload during the highest workload phase of flight; it's very likely you'd need a computer in the loop to make this concept work.
Bearing in mind the weight/complexity, c.g., safety, and control issues this brings up its worth thinking hard about what this buys you; adding a canard or a horizontal tail are much simpler ways of accomplishing the same thing.

Thanks, your positive way of thinking gives useful ideas to the table.
First, I have to disagree on the rephrasing of the question to replace canard. As this was successfully achieved on X-31, where flaps were not used for landing. My question is about flaps, which can give up to 3 times lift without landing visibility compromise at high AoA.

Exactly. I'm trying to balance the weight of the engine as prop would sit right on it.

I'm thinking of starting small. Lightweight tilting electric engine or fixed one plus EDF. In any case it should have enough thrust, to make high lift gain possible by flaps and CoG at landing manageable.

The idea is to have untrimmed elevons at cruise speeds while anything slower requires elevons up or nose down thrust.

The wording of "replace canard" may be unclear. What I meant is, on a delta wing aircraft, if you want to use trailing edge flaps to increase the lift, you have to somehow counteract the nose-down pitching moment. The "normal" way to do that would be a canard, but you're proposing to use thrust instead. In principle that is a valid choice you could make.

It's still not clear that it's one you should make though; why not just use a canard? Or why not just make the wing bigger to get the landing distance? Or use leading edge devices? I think it would be hard to show that this concept buys its way on relative to those alternatives (but not having numbers on your configuration I can't say that it doesn't, either). 3) Using elevons up when you have the flaps deployed will cancel much of the lift benefit from the flaps (since they're in the same place). You'd need to use the nose thrust; the complication being the amount needed changes w/ speed.

By this answer I'm looking for the most viable option to make fast compact delta land slow and safe. Canard had been tried by "RMT Bateleur". I believe it can be even better. If you would like to contribute, please join more practical discussion at https://www.homebuiltairplanes.com/forums/threads/can-thrust-vectoring-enable-use-of-flaps-on-pure-delta-wing.32781/

One very strong reason thrust vectoring is of little or no use to offset flap-induced pitch moment: you reduce thrust to idle or near idle during landing, which would make the thrust vectoring ineffective.
The Harrier lands at higher throttle (it takes much more than 50% power just to hover with no stores aboard).  If you were using fans at the nose, driven directly by the engine (like the front nozzles on a Harrier) you'd have high tailpipe thrust exactly when you want none.
Thrust vectoring from a jet is an unnecessary complication unless you need it either to hover or for extreme maneuverability.

Harrier uses 90% of thrust to hover being 50% under-loaded compared to rolling takeoff. Big flaps will do the half of the lift increase at the rear end of aircraft, while another equivalent part will substantially load the engine. So, idle engine should not be an issue.

You can't run the front "pump" like the Harrier uses for significant thrust without getting similarly high thrust from the tailpipe -- unless you use a completely separate forward engine, electric or hydraulic lift fan, or similar.  Overall, there's no advantage in this vs. putting a canard on for pitch control to let you use flaps the conventional way.  A canard+wing is also more efficient than a tailless wing.

You are assuming a jet engine with all of its complexities to split the power and no availability of tractor configuration with it.
But what if we consider a piston / electric tractor prop?

@AnbuAgarwal Then we have the complexity and weight of a swivel-propeller system, and a whole new universe of failure modes.  And still you reduce power/thrust to slow and descend for landing, which is when you'd need more thrust for vectoring to offset flap-induced pitch moment.

swivel-propeller is not that heavy (Joby Aviation S2 had 12 of them) and thrust is not reduced - it is rather vectored down

I'm not sure why we're assuming that flap deployment will cause pitch instability. As far as I'm aware, flap deployment moves the CoP rearward, which should make the aircraft more stable. I may be missing something here, though, I'm still working my way through Perkins&Hage. I'm not quite following Peter's argument about gusts.
For now we'll work under the assumption that extended flaps will cause a rearward shift of CoP in the pitch plane and thus increased pitch stability. However, this same rearward shift will intuitively, as you noted, cause a nose down moment, which would be aggravated if you did some kind of Fowler flap setup. This is corroborated by the above linked articles and pg.29 (pdf pg.33) of this NACA data.
Regarding your ideas to cancel this moment out to allow yourself to actually use the high cL you get from these flaps:

Ducting the jet exhaust to the front of the craft: While within the realm of physical possibility, this would likely be a highly inefficient design due to the number of sharp turns the exhaust would have to take, and the amount of heat energy it would lose while doing so. Overall, it wouldn't likely be implementable.
Additional engine: likely weight prohibitive.
Fan driven by shaft: The most reasonable of your concepts in my mind. As you noted, it's been done before. However, as far as I'm aware, the Harrier uses ducted jet flow rather than a fan. I think you're thinking of the F-35B.
Tilted prop rotor: A statically tilted rotor wouldn't do a ton at low angles, and at high angles would be extremely inefficient in forward flight.
Thrust vectoring: As others have noted, this would likely only cancel out lift gains from the flaps.
Other options: See below

Other options:

Dynamically tilting prop rotor: perhaps, But this would seem more mechanically complex to me (rotational drives, shaft bearings and CV joints, morphing ducts, keeping a healthy flow to turbine, etc.) than a seperate shaft driven fan and likely wouldn't end up saving you weight. Not worth pursuing in my mind.
Aggressive leading edge slats: It seems that leading edge slats don't have too significant of an effect on the moment of an airfoil. I haven't seen anything listed in any NACA testing I've seen, it seems like they treat it as a given that there isn't too much of an effect. This design compendium seems to agree on pg.256 (pdf pg.277).

This is all, of course, addressing your interest in using flaps as a high-lift device. You might want to think about other high-lift devices, either in their place or to mitigate their use in your design so you don't have as much of a moment increase to deal with in whichever method (shaft-driven fan, please) you might decide on if you go that route.
The first, in my mind, would be blown airfoils and related high-lift devices. You're already looking at "ducts from the engine output," you could instead throttle the exhaust of the engine and route the exhaust to slots placed midway along the wing to increase boundary layer energy, thus increasing lift. If you want to get really funky, you could look into reverse flow slots(see 4th paragraph of "mechanism" section). The paper by Wake, Tillman, Ochs and Kearny on the matter is fascinating and worth getting your hands on. I'm worried what effect swept wings (inc. delta wings) or even the lack of an high aspect ratio would have on its effectiveness, though.
Alternatively, you could look into making the exhaust a venturi vacuum generator and play with boundary layer suction. This is apparently very attractive on highly swept wings, so it might be pertinent to your design.
The Shinmaywa US-1 and US-2 flying boats use a dedicated turboshaft engine inside the hull purely to provide high-pressure air to their boundary layer control system, and the resulting STOL capabilities are mind-bending, go find some videos on it. You wouldn't be able to get that much benefit from harnessed exhaust exhaust, as the Shinmaywa uses it in conjunction with some nuts flap configurations that would be far too aggressive for your planform, but it can give an idea as to the potential of boundary layer control.
Note: sorry for the lack of sources near the end. Limited on #links until I get more rep I guess.

thanks for new ideas, @h-ramsey.
You mentioned statically tilted prop, which I agree, wouldn't help a lot, but what about dynamics, like on AgustaWestland AW609?

I actually addressed that with the first of my "other options". I feel a separate fan would likely be far more weight efficient and mechanically simple.

sorry, I should have been more specific. You say that jet engine with tilted engine / prop would be a complex endeavor due to this engine particularity. But what about electric / piston engine with tilted prop?

Hm, I wrote my initial response assuming that you were considering a purely turbine powered aircraft, looks like that was an incorrect assumption.

Sorry, unused to "enter" finalizing a text entry. Back to the point at hand, though. Are you talking about a tractor tiltrotor configuration? I can't think of any deltawinged or flying wing planes with a tractor propulsion setup off the top of my head. It might work, but you have to keep in mind that when you're tilting the rotor, the body of a flying wing would essentially work as a reverse airfoil on the propwash. I'm not sure how realistic that is. Your mention of an electric motor does bring up an interesting idea, though. If, on your main propulsion engine(s) (I'm going to keep assuming

pusher, because that's the norm for your wing layout), you have a relatively high-output electric generator, you could store a large amount of energy in batteries (Tesla battery modules are proliferating) using excess power (engine makes nearly climb power and the generator siphons off enough such that only cruise power is used for propulsion) and drive an electrically driven ducted fan for landing.

finally I have someone with positive thinking :)
I intentionally wrote the question quite open to attract ideas from different perspectives.
I was thinking about electric pusher from the beginning.
Small and light enough to easily mount on a single axis gimbal. But that is mostly due to my low knowledge about turbines.
If there would be no other ideas, I would probably edit the question to narrow down to this particular case.
This leaves the question about nose propwash and controllability, as flaperons would have to work at much lower speeds than they usually do on such aircraft.

oh, noticed a typo. Not a pusher, but a TRACTOR.
Regarding the reverse airfoil effect, the nose may be long and pointy as housing an electric motor may be pretty compact.

If you're already planning on tractor electric, then making it a tiltrotor might be the correct move for you.

My only worry is how much thrust will be needed to balance the lift from flaps. For a Cark Y airfoil, NACA data says a simple .30c split flap can increase lift by 65%. Make sure to estimate lift increase and camber changes from the flaps for your wings to see how much vertical thrust you'll need to counter it, and make sure you have enough horizontal thrust left over at that propeller angle for speed manipulation. Keep in mind that increasing throttle due to, say, a too-steep sink rate would pitch the nose up, leading to a potential stall condition.

You'd either need responsive tilt-servo-control with good controls to predictively account for this or counter-intuitive pitch-down control to the elevators (or eleflaps or whatever you'd call combined function elevator-flaps) from the pilot or fly-by-wire system.